Hitler's troops stole the jewel-encrusted chamber in 1941 — reportedly packing it up into 27 crates — and shipped the treasure to Koenigsberg. It later disappeared, sparking numerous theories about what happened to the fabled treasure.

Karl-Heinz Kleine has been aiding in the search — which recently took on a patch of forest — thinks a large munitions factory on the outskirts of the town of Wuppertal might hold the key. The factory boasts a huge underground bunker with secret passageways.

"That would be my choice to hide a treasure like the Amber Room," he told NBC News. Kleine and his fellow treasure hunters are certain that they will find "something" once they make it down to the bunker — but say they need more high-tech instruments to help.

"We have the local knowledge but we really need ground radar now to speed things up," he explained.

If the bunker doesn't pan out, there’s still an underground train — with blocked off entrances — containing mysterious boxes that could offer clues in the search for hidden Nazi treasure.